The invention relates generally to the field of power systems, and more particularly to impedance measurement techniques for determining the stability of power systems.
Power systems are incorporating a greater degree of electronic circuits, power electronic converters and electronic switching sources and loads. Although these components improve the performance of a power system, they are prone to instability due to their high efficiency and constant power characteristics which may lead to a negative impedance nature. The instability of these components affects the stability of the overall power system. Power system stability can be determined from the source and load impedances of the system. Thus, impedance measurement techniques for determining power system stability are becoming increasingly important in many applications; particularly in naval ship and aerospace power systems.
Considerable research is being done on impedance measurement techniques that extract and measure the impedance of power system sources and loads to determine power system stability. Some effective impedance measurement techniques include current injection and voltage injection. For example, current injection techniques have been used to measure the impedance of a load and a source in a three phase alternating current (ac) circuit. However, prior current injection techniques of three phase ac circuits, as illustrated in FIG. 1, are not very efficient. Some of the problems caused by prior current injection techniques in three phase ac circuits are that the current must be injected at all phases of the circuit. Additionally, hardware implementation is difficult because of a complex hardware configuration. Further, the current being injected in the circuit is difficult to control.
These problems tend to limit the effectiveness of prior art current injection techniques of multi-phase ac circuits in applications where efficient and accurate determinations of power system stability is desirable.